This sure does ound like a lint build up! Both of my Viking machines hate lint and well act mean and nasty if they are not well 'dusted'. You can probably de-lint your machine yourself.
Also, if you have an older machine, do you have to oil it (ONLY after delinting tho)? Check your user's manual for this info.
Only other things I can think to check and re-check is the needle - is it dull or bent? Changing needles often is a must for my machines also.
The next would be professional sevicing needed. I hope that is not it.
Let us know what happens on this.
Julie